In 1970 I was working in our family's auction house. I bought a small box of HO stuff. Included was a Revell HO 0-6-0 which had no cab.
I ground the domes and stack off the metal body. Added some Kemtron O scale domes, stack and headlight.
I scratched an O scale cab and ended up with an On 2 1/2 locomotive.
My model railroad friends thought I was stupid and wasting my time. But I didn't care as I was having lots of fun.
Before long I removed the cab from a Matua 0-4-0 diesel and scratched an O scale cab.
I had an Atlas 0-6-0 in N scale and added HO Kemtron cab, domes, stack and headlight. photo attached.
I have been in narrow gauge ever since. All the people who made fun of me are dead and I am still having fun.
But my toys are much more expensive now. Currently working on a 1/20.3 Mich Cal shay #2.